Molding Difficult Patterns

Description

Molding Difficult Patterns

Use of Green-Sand Ring. In the small sheave pulley, Fig. 120, we have an example of a casting the construction of the pattern for which, so as to make it easily removable from the sand, may give some trouble to the beginner. The pattern is shown in cross-section in Fig. 121, and is molded in a two-part flask. At first it would seem impossible to place the pattern in the sand so that either half could be removed when the cope and drag are separated on the parting line of the pattern. This is readily accomplished, however, as follows:

Fig. 120. Sheave Pulley.

The half pattern C is placed in the inverted drag, with the parting downward on the molding board, and is rammed up in the usual way. After the drag is turned over, the sand is cut away and removed to the center of the rim edge, as shown in Fig. 122. The cut is carefully smoothed, and parting sand applied to the cut surface. The part a of the pattern is placed in position on c, and is rammed up carefully, the sand being then cut away to the center of the rim edge of A. Parting sand is applied to the new surface, after which the cope is placed in position and rammed up. When the cope and drag have been separated, the upper half A of the pattern is taken out, and the cope is returned to its place on the drag. The whole flask is now turned over, and the drag lifted off the cope, when the ring of green sand Z, Fig. 123, will rest on the cope sand and the part C of the pattern is taken out. We thus have two partings of the sand mold, but only one parting of the flask.